When producing oil from an oil field, water and/or steam may be injected into the injection well to drive the production of oil. The oil is pressed by the water, steam, steam foam or froth and/or other driving fluid through the geological layers into the oil production well, thereby enhancing the production of crude oil. Stimulation of oil production by injection of driving fluid into the formation is a technology used in so-called Improved Oil Recovery (IOR).
In a stratified oil-bearing formation the permeability of different geological oil-bearing layers may differ, which has as result that injected water will reach the production well initially through the most permeable layer, before a substantial amount of the oil of the other, less permeable, layers is retrieved. This breakthrough of injection water is a big disadvantage, as the water/oil ratio retrieved from the production well will rapidly increase and become more and more unfavourable during the lifetime of the oil field.
It is known in the art to insert an annular plug in an inflow region of an oil production well to shut off the layer with the injection water break-through. Such an annular plug can be applied by locally providing a cement lining, which seals off the respective layer. It is however difficult to determine the position of this layer, such that generally several attempts have to be made before the flow of the layer is reduced. In some circumstances however the water producing layer cannot be identified and/or the placement of a cement plug cannot be performed.
U.S. Pat. No. 5,291,949 discloses a method to inhibit a caustic flood breakthrough at a production well. When a caustic flood occurs or is imminent at the production well, three slugs of fluid are injected into the formation via the production well. First, a slug of a spacer fluid such as oil or other hydrocarbon. Second, an acidic solution comprising a crosslinkable polymer and a lanthanide. And third, another oil or hydrocarbon spacer fluid to displace and push the second fluid into the formation. When the caustic flood contacts the acidic solution inside the formation, the pH of the solution is raised. At the raised pH the lanthanide can crosslink the polymer to form a gel, which inhibits the caustic flood from reaching the production well.
The known method is expensive and complicated. Expensive chemicals (polymer and lanthanide) are used in the second fluid and the use of spacer fluids is required so as to arrange that a cross-linking reaction of the polymer occurs upon raising of the pH.
It is therefore an object of the invention to provide a method, which alleviates the above mentioned disadvantages.